This invention relates to improved packing materials for gas-liquid contacting in packed towers, cross flow tray columns, motionless mixers and like apparatus.
Chemical processing apparatus frequently includes towers filled with a packing material which provides many liquid-supporting surfaces. Liquid introduced at the upper end of the tower flows downwardly as a thin film on the surfaces of the packing material. Gaseous vapors are injected into the lower end of the tower and ascend through spaces in the packing material, moving through the tower in intimate contact with the liquid film on the surface of the packing. The contact between the liquid and vapor can produce a variety of effects such as mass transfer, chemical reactions, heat exchange and scrubbing or deentrainment.
Considerable efforts have been devoted to the development of packing materials which provide a reasonable latitude of gas and liquid throughput, a high mass transfer rate and a low pressure drop. Random packings formed of loose rings, cylinders or saddles are commonly used; and, packings of preformed sections which extend the full transverse extent of the tower have been developed as exemplified by U.S. Pat. Nos. 3,285,587 and 3,927,165.
There have been some efforts to develop packing materials which, like the present invention, are formed of parallel sheets of expanded sheet material such as expanded metal. Such sheets are manufactured by forming staggered parallel rows of longitudinally aligned slits in a flat continuous sheet of metal and then deforming the sheet to lenghen it transversely of the openings and open the slits to create diamond or almond-shaped openings. The openings are disposed in rows which angularly intersect. The strips of metal between the openings become canted relative to the plane of the panel, and they take on an undulating configuration. Each strip may be regarded as having successively arranged sets of four segments, in which the first and third segments define the edges of the openings and the second and fourth segments are connected to the opposite segments on the adjacent strips. Segments of the undulating strips are aligned to form two intersecting sets of parallel linear strips which lie between and define the angularly intersecting rows of openings.
British Pat. Specification No. 427,087 discloses a scrubber formed of a stack of sheets of expanded metal, preferably vertically disposed with the short lengths of the diamond shaped openings of successive sheets being oriented so that one sheet has its short mesh vertical, the next sheet has its long mesh vertical, the next sheet is reversed and has its short mesh vertical, and the next sheet is reversed and has its long mesh vertical.
British Pat. Specification 977,752 of 1964 discloses a packed tower in which stacks of expanded metal sheets have their stretching directions alternately horizontal and vertical. The planes of the panels in alternate layers lie at right angles to the planes of the panels in the other layers. A panel which directs liquid droplets toward the vertical central plane is situated next to a panel which causes the droplets to travel more toward the center of the tower.
British Pat. Specification No. 734,874 of 1955 relates to a tower packing formed of layers of expanded metal sheets which are somewhat nested and oriented so that the inclined webs in one layer are oppositely inclined to those in the adjacent layer, thereby producing a louver effect on the gas which flows in a general direction perpendicular to the layers.
Although the foregoing discussion has dealt primarily with packed towers, it is believed that the invention is also suitable for use in connection with cross flow tray systems such as those shown in U.S. Pat. No. 4,105,723, conduit-connected motionless mixers of the genre exemplified by U.S. Pat. No. 3,286,992 and other types of apparatus.
The invention also relates to dualflow tray devices wherein liquid descends and vapor ascends through the same apertures which collectively provide an open area no greater than about 40% of the total tray area. Heretofore, dualflow type trays in large diameter columns have been found to be unsatisfactory due to instabilities in the liquid bed.